The increase of atopy and allergic disease is a global tendency, and 30 to 50% of the whole population are estimated to be atopic (non-patent ref. 1 which is listed hereinafter). The atopy indicates a condition wherein IgE is inclined to be generated against foreign antigens and Type 1 allergy is inclined to be caused. The typical diseases of Type 1 allergy are allergic rhinitis, allergic bronchial asthma and allergic conjunctivitis, which are caused by airborne particles containing antigen. Included among such airborne particles are, house dust whose important constituent is dust mites, and which is mentioned in a perennial case, and pollen which is mentioned in a seasonal case.
Perennial Allergic Rhinitis
Allergic disease shows a tendency of increasing and house dust mite allergy is recognized as a global health problem by WHO (non-patent ref. 1 below).
According to the allergy skin prick test among adults in south west London, the proportion of subjects with at least one positive reaction (that is the diameter of weal caused by grass pollen, house dust, or house dust mite antigens is larger than 1 mm), showed a significant increase from 23% ( 312/1359) in 1974 to 46% ( 34/74) in 1988 (non-patent ref. 2). According to the follow-up survey of the allergy skin test that was carried out on 1333 subjects aged 3 years and more, in Tucson, Ariz., during 8 years on average, the proportion of subjects with at least one positive reaction to plural antigens increased from 39.1[%] to 50.7% (non-patent ref. 3).
Furthermore, the proportion of the complicated cases of perennial allergic rhinitis and pollinosis is large. According to the postal questionnaire to adults aged 16 to 65 years in London, 55% of 1309 subjects with rhinitis had perennial symptoms only, 11% seasonal symptoms only, and 34% had the complicated symptoms of them (non-patent ref. 4).
In Japan, the estimated national prevalence of perennial allergic rhinitis in 1998 is 19.8%, and the estimated prevalence of Japanese cedar pollinosis is 17.3% (non-patent ref. 5). In addition, about 37% of perennial allergic rhinitis are in the complication of Japanese cedar pollinosis, which is based on the complication rate of these two allergic rhinitis by age groups, and others (non-patent ref. 6).
In perennial allergic rhinitis and allergic bronchial asthma, the dust mite allergen scattering from bedding is the matter of great concern. The dust mite allergen is contained in the fragments of the dead bodies and feces of mites. They break into particles with an aerodynamic diameter of over 1 or 2 μm and scatter (non-patent ref. 7). According to the example of measuring the aero-concentration of DerI and DerII as major allergens, the aero-concentration at the place near a sleeper's head and 30 cm high above a quilt is about 10 times as large as that at the place a little high above a usual floor (non-patent ref. 8). From the viewpoints of the length of sleeping hours and the situation in which the respiratory organs are close to bedding, it is understood how serious it is for the dust mite allergen to scatter from bedding.
Allergen exists in nightclothes also. The DerI concentration of the fine dust got from nightclothes is over 2 μg/g fine dust on average, which can induce allergic symptoms (non-patent ref. 9).
A Hybrid Air Cleaner
It is known that the symptoms of perennial allergic rhinitis are reduced if bedding is cleaned with a vacuum cleaner. However, it is hard to get into the habit of cleaning bedding with the vacuum cleaner of a floor movable type or a stick type. The vacuum cleaner of a handy type, which integrally has a motor and a paper dust pack, is too heavy to be easily handled.
Furthermore, although the dust mite allergen exists mainly inside bedding, cushions and others, rather than on the surface of these, removal of the inner allergen effectively with the existing vacuum cleaner has not been achieved.
The patient of perennial allergic rhinitis uses an air cleaner while sleeping, so it is useful that the air cleaner is equipped with a light allergen suction device and bedding is easily cleaned. In this case, dust sucked from bedding is too heavy a load for an air filter, so it is necessary to install a pre-collector which can collect comparatively large particles in upstream of the air filter.
As separators which collect comparatively large airborne particles, there are a cyclone, a multiclone, an inertial separator with a duct (for example, U.S. Pat. Nos. 3,710,561, 4,971,604 and Japanese Patent Examined Publication S52-29277) and a renewable filter, for example a wire mesh of stainless steel and so on.
The apparatus disclosed in the U.S. Pat. No. 3,710,561, shown in FIG. 41(a), is a dust collector having a rectangular duct with continuous curvature and spanwise channel width larger than radial, and having an aperture on an outside adjacent to an outlet.
The apparatus disclosed in the U.S. Pat. No. 4,971,604, as shown in FIG. 41(b) removes mineral fibers that are pneumatically transported. A duct with a square or rectangular section is curved by 90° and an air flow passes through an exhaust portal, with particles getting to an output portal.
A representative dust collector is a cyclone or a multiclone comprising a plurality of cyclones in parallel. Although the collection efficiency of them is high, yet pressure loss is large. A tangential inlet cyclone is used usually at an inlet flow velocity of 7 to 15 m/s, and according to Iinoya's formula, the pressure loss of the above cyclone having a standard size ratio is about 240 to 1100 Pa with an outlet pipe open to the atmosphere (non-patent ref. 10).
Furthermore, a high-velocity swirling flow at an exit of the cyclone is extremely turbulent, which is not preferable for an input of a backward air filter.
Therefore, when the cyclone or the multiclone is used as a pre-collector upstream of the air filter, the suction power of the allergen suction device becomes weak. Furthermore, a household air cleaner is generally equipped with a fan whose wind flow rate is large and static pressure is low, so in a case where a flow to deal with by the allergen suction device ranges, the cyclone becomes unable to deal with a large flow.
Next, the method of separating particles from the air with a curved duct is described. Although the curved duct has the advantage that pressure loss is small, yet the collection efficiency of particles is not good owing to the turbulence of flow caused by centrifugal force.
When particles and so on are separated from the air by the curved duct with a circle or square section (for example, Japanese Patent Examined Publication S52-29277), a secondary flow, a velocity component, that is perpendicular to a direction of a main stream, develops, so the collection efficiency falls. The secondary flow is a phenomenon that is caused by the difference of a radial fluid thickness and the presence or absence of a sidewall friction.
The duct shown in FIG. 41(b) is also much affected by the sidewall friction. Furthermore, even if the duct is provided with a collection chamber at the output portal, particles separated from the air flow tend to re-scatter, because a collection mouth is wide.
On the other hand, in a curved rectangular duct with high aspect ratio, the effect of friction is restricted to the neighborhood of a sidewall and different flow phenomenons emerge over an outside concave wall and an inside convex wall. Concerning the stability and unstableness of a concentric flow, such things as the following are considered by persons, from Prandtl down (non-patent ref. 11).
When a fluid mass moves circularly at a radius y and with a velocity U, centrifugal force is balanced against pressure gradient. Therefore, let p and ρa be pressure and air density, respectively, andρa(U2/y)=dp/dy holds. Let U1 and U2 be the velocity at a radius y1 and y2, respectively. Now, when a fluid mass at the radius y1 moves to be at the radius y2 and the velocity U1 becomes U′, angular momentum is conserved like the next,ρay1U1=ρay2U′. At this time, centrifugal force acting on the fluid mass having moved isρa(U′2/y2)=ρa(y1U1/y2)2/y2.If this value is smaller than the pressure gradient at the radius y2, ρaU22/y2, that is y1U1<y2U2, the turbulence goes toward restoration, with the result that the flow becomes stable. Conversely, the former is larger than the latter, that is y1U1>y2U2, the turbulence goes toward increase, with the result that the flow becomes unstable. To be brief, in the concentric flow, when angular momentum radially increases, the flow becomes stable, and when angular momentum radially decreases, the flow becomes unstable.
In the curved rectangular duct with high aspect ratio, taking a radial distribution of a main stream velocity into consideration, a side to fulfill the stability condition that angular momentum increases is a convex wall side, and the one to become unstable is a concave wall side.
This is proved by the many experimental results of the past. In a boundary layer over a concave wall, there often occur Görtler vortices, the counter-rotating longitudinal vortex pairs whose axes are parallel to the direction of the main stream. The Görtler vortices are stationary longitudinal vortices that occur in a transition process from a laminar flow to a turbulent flow in the boundary layer, and it is also observed in a turbulent boundary layer. It is difficult to predict the occurrence of the Görtler vortices. The occurrence is much influenced by an overall apparatus configuration and turbulence at an entrance, and the vortices occur in some cases and do not occur in other cases. Even if the stationary vortices do not occur, the turbulence over the concave wall, which is caused by centrifugal force, is large.
To the contrary, a turbulent flow is further suppressed over the convex wall, which has been made clear by (a) a flow visualization with a smoke wire method and (b) the measurement of turbulent energy (non-patent ref. 12, non-patent ref. 13).
When particles are separated from the air flow by a curved rectangular duct with high aspect ratio, a flow turbulence over the concave wall of a duct like FIG. 41(a) is large, so a particle separation efficiency is not good. In addition, a plurality of prominent blades themselves disturb the current. Further, in this apparatus, even if it is equipped not with plural collection mouths but a single narrow collection mouth, the collection efficiency is low. Further, even if it is equipped with a wide collection mouth, the collection efficiency is not good because of the re-scattering of collected dust.
The above is the major problem wherein particles are inertially collected from the air with the duct.
Furthermore, the conventional inertial dust collector with the duct has a problem wherein a particle with large inertia and unfixed form tends to escape. When the diameter or velocity of a particle increases, which means a particle inertia increases, the particle property of following a current decreases and that of moving straight increases. In addition, a particle with a non-spherical or unfixed form irregularly bounces on a wall surface. For that reason, in the duct shown in FIG. 41(a), such particles tend to pass over the collection part. In the duct shown in FIG. 41(b), particles, which somewhat obliquely enters from an inlet, bounce on an outside wall, occasionally escaping. The phenomenon that hard coarse particles bounce on the wall surface and escape is observed in the cyclone also. The reason why the collection efficiency of the cyclone with a cylinder diameter less than 100 mm does not necessarily progress is believed to be due to the bounce of particles on the wall surface (non-patent ref. 14). Because an air filter is used downstream in a hybrid air cleaner, such particles that have escaped become the load of the air filter in full.
Next, a case where a renewable filter is used is described. When the renewable filter is used, collected dust is accumulated according to the use with the result that the suction power of the allergen suction device falls. Further, it has the problem of quickening the degradation of a deodorizing filter because the flow passes through the collected dust. In addition, it has a non-sanitary aspect where unwanted bacteria breed according to the temperature and humidity after water washing.
Furthermore, when particles with a diameter smaller than 20 μm are collected by the wire mesh of stainless steel, pressure loss gets large. The typical weaving patterns of wire meshes are plain weave, twill weave and twill Dutch weave. The plain or twill weave is the weaving pattern where every warp or weft is woven with separation. Although its pressure loss is small, a minimum aperture is 20 μm. The twill Dutch weave is the weaving pattern where wefts touch each other and a small wedge-shaped aperture, which is made up of a warp and a weft, plays a part as a filtering hole. Although its minimum filtering diameter can be under 20 μm, the pressure loss is large. The pressure loss of the twill Dutch wire mesh with a filtering diameter of 20 μm is 6 to 7 times larger than the twill wire mesh with a aperture of 20 μm. In bedding and so on, particles with a diameter smaller than 20 μm, which settled from atmospheric aerosol, are much contained. Pressure loss gets large when the twill Dutch wire mesh is used.
By the way, in a season when pollen scatters, pollen which adhered to hair or clothes during the patient's outdoor stay is carried indoors, and it re-scatters from them also. Pollen which re-scatters from hair passes in the neighborhood of the patient's eyes and/or respiratory organs, easily inducing allergic symptoms. The number of female patients with Japanese cedar pollinosis, aged 10 to 49 years, is greater than that of male patients (non-patent ref. 2, non-patent ref. 15). Woman's hair is so long and rich that pollen tends to adhere to it and go deep into it. Further, pollen which has invaded indoors and deposited on a sofa, bedding and so on, re-scatters from them during their use, inducing allergic symptoms. It is desirable to remove such pollen effectively, but a method or an apparatus for it is not presented.
Lastly, air blowing and circulation is mentioned. Although a conventional air cleaner circulates and purifies an air of a whole room, yet to remove the allergen suspending near the respiratory organs of the patient of perennial allergic rhinitis during his or her sleep, which is most important for the patient not sufficiently done.